1. Field of the Invention
The present invention relates generally to nondestructive testing, and more particularly to a finger-tip probe for nondestructive testing which comprises a flexible sensor.
2. Description of the Related Art
In the field of nondestructive testing (NDT), ultrasound and eddy current techniques are commonly used to characterize material properties and detect flaws in parts under inspection. Ultrasound, which is typically used for volumetric inspection, involves the generation and detection of ultrasonic waves in a part with an ultrasonic transducer. Eddy current methods, which are commonly used to inspect the surface of a part, involve the electromagnetic induction of eddy currents within the part using a changing magnetic field, and the detection of eddy current effects to determine part characteristics or flaws.
Performance of many NDT systems can be improved by placing the sensors in direct contact with the part under inspection, because commonly the inspection sensitivity is directly related to the placement, proximity, and coupling of the sensors to the surface of the part. The accuracy of NDT techniques may thus be influenced by geometrical constraints of the probe which houses the sensor and the exterior boundary conditions of the part. The exterior boundary conditions may include, for example, surface curvature, which may introduce limitations to the performance of the inspection system. Other exterior boundary conditions include surface roughness, external coatings, support structures, corrosion, and fasteners.
To provide flexibility in inspecting parts having a surface curvature, known systems utilize a flexible eddy current coil or ultrasonic sensor integrated into a multilayer flexible polymer film. This arrangement, which enables the sensors to be efficiently coupled to a curved part, eliminates the need to maintain a large inventory of probes tailored to fit individual geometries and curvature conditions of various parts.
Another factor which influences the sensitivity of the sensor is the pressure with which the sensor is applied to the part. A uniform pressure properly couples the interactions between the sensor and the part under inspection. Uniform pressure reduces variations in signal response to factors not directly related to the detection of material flaws or material properties. To achieve a uniform pressure at different inspection sites, a known solution utilizes compressed gas at a controlled pressure applied against the back of a flexible eddy-current sensing coil array. The eddy current sensing coil array is disposed in an eddy current probe which is under the control of a multi-axis mechanical control system which precisely manipulates the probe over the part. The complexity of such a system, however, may limit its usefulness due to cost considerations. The size of the system may also limit its accessibility to remote parts.
Hand held probes are known which provide NDT data without the substantial cost associated with a multi-axis control system. One known hand held probe includes a mechanism for applying a uniform pressure to the part surface, which pressure is decoupled from the pressure the operator uses to apply the probe against the part. Hand held probes, however, typically include a supporting structure which limits the accessibility of the probe to remote regions of a part and which makes the probe somewhat cumbersome to use.
It would be desirable, therefore, to have an inspection apparatus which was able to reach relatively inaccessible regions of a part and apply a uniform pressure to the surface of the part at a low cost.